When an uncharged metallic sphere A is brought near a positively charged metallic sphere B, then 

Negative charge is induced on the nearer surface of A and equal amount of positive charge is induced on the surface which is away from B. Potential of A due to induced charges does not change but due to the positive charge on B, potential of A increases. 

Since the induced negative charge on A is nearer to B and induced positive charge is away from B, potential of B decreases.